Risk of fuel boost pump unporting with low fuel levels and uncoordinated flight - Civil Aviation Safety Alerts (CASA) No. 2018-11
Owners, operators and maintainers of Bell helicopter model 206A, 206B (including 206B3 commercial designation), and 206L, 206L-1, 206L-3 and 206L-4 helicopters
|File Classification No.:||Z 5000-35|
|Document No.:||CASA 2018-11|
The purpose of this Civil Aviation Safety Alert (CASA) is to raise awareness of the risk of engine flameout associated with uncoordinated flight with a low fuel level that could result in unporting of fuel boost pumps.
There have been several Bell Helicopter model 206 series accidents and incidents involving fuel starvation and loss of engine power. When the loss of engine power occurred during low level flights, it resulted in forced landings of the helicopter.
Following the accident of a Bell 206B at Fox Creek Airport in Alberta on September 5, 2016, the Transportation Safety Board of Canada (TSB) issued Aviation Safety Advisory A16W0126-D2-A1 to Bell Helicopter Textron Canada Limited (BHTCL) recommending the amendment of the rotorcraft flight manual (RFM) to include a 20USG caution even if a fuel low caution light system is installed.
The TSB accident investigation confirmed that it is important for operators to understand specific aspects of the Bell 206B fuel system design and the risks associated with flights conducted with less than 20USG of fuel on board.
Transport Canada has further determined that the Bell 206A, 206B3 and 206L- series models may also exhibit the same risk due to their similar fuel system designs.
Bell 206 series helicopters are used to conduct a variety of aerial survey work and agricultural aerial spray applications. Such operations require sharp turns/maneuvers resulting in increased momentary lateral acceleration forces causing fuel migration. If the fuel level is low, this can cause unporting of the fuel boost pumps and a sudden loss of power. Transport Canada also notes that some of these flights are intentionally conducted with minimal amount of fuel on-board in order to maximize payload, which may further increase the risk of unporting of the fuel boost pumps.
Furthermore, some of these operations call for the helicopter to operate in the shaded area of the Height-Velocity (H-V) diagram where it would be difficult or impossible to successfully carry out an autorotation following an engine flameout. This additional risk is apparent in previous accident reports showing substantial helicopter damage and severe injury to occupants.
As a result of the TSB Aviation Safety Advisory, BHTCL has amended the Bell 206A, 206B, 206B3 RFMs to incorporate the following changes:
- Use of consistent terminology in the RFMs for the criteria of “Land as soon as practical” when the fuel low Caution light (if installed) illuminates;
- Introduction of a warning in Section 2 of the RFMs to address rotorcraft that do not have the fuel low caution light system installed, highlighting to avoid uncoordinated turns/maneuvers with a low fuel quantity.
The 206L and 206L-1 RFMs will also be amended with similar warnings as the 206L-3 and 206L-4, to avoid uncoordinated flight with fuel low caution as fuel starvation may occur.
To reduce the risk associated with unporting of fuel boost pumps at low fuel levels resulting in engine flameout, Transport Canada recommends the following:
- Ensure that the minimum fuel quantities recommended in the RFM are observed;
- Always follow the RFM operating procedures with regards to fuel low Caution, if the fuel low Caution light system is installed;
- Install a low fuel warning device such as the fuel low Caution light system in accordance with BHTCL Technical Bulletin 206-84-94 or 206-85-113, as applicable. This is especially recommended for Bell 206A/206B operators that frequently conduct flights with near minimum fuel quantities on board.
- Avoid uncoordinated turns/maneuvers with a low fuel quantity; and
- Incorporate the amended RFM as detailed below, or later revisions approved by Transport Canada, and inform the flight crew of the changes:
- BHT-206A-FM-1, Revision D-48, dated 23 April, 2018
- BHT-206B-FM-1, Revision B-54, dated 30 May, 2018; and
- BHT-206B3-FM-1, Revision 17, dated 30 May, 2018
Of note, the above amended Bell 206B and 206B3 RFMs have been previously mandated by Transport Canada Airworthiness Directive (AD) CF-2018-23 to address an unrelated unsafe condition.
Transport Canada continues to monitor events related to this issue and will issue recommended or mandatory corrective action, as necessary.
For more information concerning this issue, contact a Transport Canada Centre; or contact Audrey Vézina-Manzo, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639, facsimile 613-996-9178 or e-mail email@example.com.
Original signed by
Chief, Continuing Airworthiness
National aircraft certification
The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.